Messages in this thread |  | | Subject | Re: [fuse-devel] [PATCH] FUSE/CUSE: implement direct mmap support | From | Miklos Szeredi <> | Date | Wed, 10 Feb 2010 09:40:24 +0100 |
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On Wed, 10 Feb 2010, Goswin von Brederlow wrote: > Tejun Heo <tj@kernel.org> writes: > > > Implement FUSE direct mmap support. The server can redirect client > > mmap requests to any SHMLBA aligned offset in the custom address space > > attached to the fuse channel. The address space is managed by the > > server using mmap/munmap(2). The SHMLBA alignment requirement is > > necessary to avoid cache aliasing issues on archs with virtually > > indexed caches as FUSE direct mmaps are basically shared memory > > between clients and the server. > > > > The direct mmap address space is backed by pinned kernel pages which > > are allocated on the first fault either from a client or the server. > > If used carelessly, this can easily waste and drain memory. > > Currently, a server must have CAP_SYS_ADMIN to manage dmmap regions by > > mmapping and munmapping the channel fd. > > Does that mean that for example in unionfs-fuse when a user wants to > mmap a file I can just mmap the actual underlying file from the real > filesystem and any read/write access would then shortcut fuse and go > directly to the real file?
No. It is the /dev/fuse file descriptor that is being mapped to give access to the "direct mmaped" memory.
Thanks, Miklos
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